Communication method

ABSTRACT

In a first microcomputer, a communication function is provided for outputting a data signal having a transmission period Tr that has a relation of Td&lt;Tp/2 with a data time Td, and it sends various data processed by itself and carried on the data signal to a second microcomputer, where the received data signal is sequentially stored in a memory, and the various data are read by timing pulses for reading and processed.

TECHNICAL FIELD

This invention relates to an occupant protecting device equipped withair bags for protecting occupants, for instance, in the event of a crashof vehicles, and related to the communication system between the mainECU (Electronic Control Unit) and the satellite ECU, which are formingthe control system of the device

BACKGROUND ART

In the communication system applied to the occupant protecting devicefor vehicles, a collision is generally detected by the accelerationsensors each provided in the main ECU and the satellite ECUs, andsignals are exchanged between the two to process the result of collisiondetermination or temporary data for the crash in the main ECU.

FIG. 1 is a schematic perspective plan view showing the positionalreplacement between the main ECU and satellite ECUs on a vehicle. 10 isa vehicle, 11 is the front portion, 12 is the rear portion, and 13 a and13 b are the side portions. A main ECU 20 is installed in the centralportion of the vehicle 10, and side satellite ECUs 30 a and 30 b areinstalled on the side portions 13 a and 13 b, respectively. Further, atboth sides of the front portion 11, there are provided front satelliteECUs 40 a and 40 b, respectively. The main ECU 20 has a function ofdetecting a collision occurred at the front side of the vehicle tounfold air bags in front of occupants, particularly the driver and thepassenger-side occupant, and a function of receiving collisioninformation from the other satellite ECUs 30 a, 30 b, 40 a, and 40 b tounfold the air bags on the side or in front of occupants. The sidesatellite ECUs 30 a and 30 b are to detect a side-impact collision by anacceleration sensor, and has a function of determining the accuracy ofthe collision by its own microcomputer and sending it to the main ECU 20through communication lines 31 a and 31 b. Further, the front satelliteECUs 40 a and 40 b are provided, because an offset collision may not bedetermined only by the main ECU 20, and they have a function ofprocessing the detection status of the acceleration sensor provided inthem by their own microcomputers, and sending the processed data to themain ECU 20 through communication lines 41 a and 41 b.

Data sent from the satellite ECUs 30 a, 30 b, 40 a, and 40 b to the mainECU 20 represent the determination result of collision and the faultdiagnosis status of the acceleration sensor under normal conditions.Thus, in the conventional communication system, a trigger signalfunctioning as a data request command is sent from the main ECU 20 tothe satellite ECUs 30 a, 30 b, 40 a, and 40 b, and the respectivesatellite ECUs 30 a, 30 b, 40 a, and 40 b transmit a collisiondetermination result or a fault diagnosis result to the main ECUaccording to the trigger. The main ECU 20 processes and determines thetransmitted result, displays a warning or unfolds an air bag.

FIG. 2 is a block diagram showing the schematic circuit configurationfor implementing the conventional communication system. In this figure,the required minimum main ECU 20 and satellite ECU 30 in a pair areshown for simplicity.

In the figure, 1 is the battery of the vehicle, by which a d.c. currentis supplied to the booster circuit 21 of the main ECU 20 via an ignitionswitch 2. 3 and 4 are squib resistances for igniting the gun powder forunfolding the air bags (not shown) for protecting the front portion andthe side portion of an occupant. If a collision occurs at the front sideof the vehicle, an ignition current is supplied to the squib resistance3 from the booster circuit 21 through a mechanical acceleration switch27, which closes when it senses an impact in the longitudinal directionof the vehicle, and a switching transistor 28 controlled by amicrocomputer 23. To the other squib resistance 4, an ignition currentis also supplied from the booster circuit 21 through a switchingtransistor 29 controlled by the microcomputer 23 upon the occurrence ofa side-impact collision to the vehicle. Further, from the boostercircuit 21, a d.c. voltage is supplied to fixed-voltage circuits 22 and32 functioning as the d.c. power supplies for the microcomputers 23 and33 and other circuits.

Now, the operation is described.

The microcomputer 23 always determines faults of a longitudinalacceleration sensor 24 in the normal condition where there is nocollision, and if a fault occurs, it outputs a signal for controlling analarm (not shown) such as a lamp. If a collision at the front side ofthe vehicle occurs, the microcomputer 23 determines the detection signalfrom the longitudinal acceleration sensor 24, which represents acollision state, and outputs a control signal to bring the switchingtransistor 28 into conduction. At this point, if the mechanicalacceleration switch 27 is closed, an ignition current is supplied to thesquib resistance 3 to unfold the air bag in front of the occupant.

Further, the microcomputer 23 exchanges signals with a communicationcircuit 25. Based on a clock pulse, a trigger signal (a) of FIG. 3 of afixed period is sent from the communication circuit 25 to the sidesatellite ECU 30 side through a communication interface 26. As describedlater, a signal (b) or (c) of FIG. 3 sent from the satellite ECU 30 inresponse to the trigger signal is provided to the microcomputer 23through the communication interface 26 and the communication circuit 25.

In the satellite ECU 30, the microcomputer 33 performs the normal faultdiagnosis of a lateral acceleration sensor 34 and an acceleration switch37, and determines the detection outputs of the lateral accelerationsensor 34 and the acceleration switch 37, if a collision at its lateralside of the vehicle occurs. In the fault diagnosis, the signal (b) ofFIG. 3 is sent to the main ECU 20 side via a communication circuit 35and a communication interface 36, and if the microcomputer 23 determinesthat an abnormal state has occurred, the alarm is operated to alert theoccupant to it. Further, in the event of a side-impact collision,determination is made in the microcomputer 33 upon receipt of thedetection signals of the lateral acceleration sensor 34 and theacceleration switch 37, and the signal (c) of FIG. 3 indicating acollision is sent to the microcomputer 23 through the communicationsystem. Upon receipt of this signal, the microcomputer 23 determineswhether the collision has actually occurred, and outputs a controlsignal to turn on the switching transistor 29 if it determines that thecollision is dangerous. Whereupon, an ignition current flows through thesquib resistance 4 via the switching transistor 29 to unfold the air bagfor side protection.

The conventional communication system is described according to FIG. 3.A trigger signal (a) of repetitive pulses with a fixed period TO isalways sent from the main ECU 20 to the satellite ECU 30 side. On theother hand, a diagnosis data provided by checking the fault status ofthe lateral acceleration sensor 34 and the acceleration switch 37 areoutputted from the microcomputer 33, and upon the reception of apredetermined number of pulses of the trigger signal (a), a responsesignal (b) including the diagnosis data is sent from the communicationcircuit 35 to the main ECU 20 side. The response signal (b) is providedto the microcomputer 23, which determines the diagnosis data, and issuesa control output to drive the alarm if there is anything wrong. Further,if a lateral collision occurs with a vehicle, the response signal is asshown by (c).

Since the conventional communication system is constructed above, themain ECU requires a transmission process for always sending the triggersignal, and a data reception process for the response signal, so theprocessing is complicated. Furthermore, there is a problem that thesatellite ECU requires a circuit for receiving the trigger, causing anobstacle to the downsizing of the device.

This invention was accomplished to solve the above described problem,and its object is to obtain a communication system in which thecommunication between the main ECU and the satellite ECU is carried outby the start-stop synchronization communication provided in themicrocomputer.

DISCLOSURE OF THE INVENTION

The communication system related to this invention comprises a firstmicrocomputer having a communication function for outputting a datasignal having a data time Td and a transmission period Tp, which sendsvarious data processed by itself and carried on the data signal, and asecond microcomputer for receiving and sequentially storing data signalsin a memory, and reading and processing the various data by timingpulses, and it is characterized in that the data time Td and thetransmission period Tp have a relation of Td<Tp/2.

With this, the start-stop synchronization communication functionprovided in the microcomputer can be directly used to construct thedevice in a small size without requiring the trigger signal as in theprior art, and data reception can be automatically carried out, so thereis an effect that the processing can be simplified. Further, the datatime Td and the transmission period Tp are provided with the relation ofTd<Tp/2, and thus, there is an effect that reception recovery can bemade faster against a noise included during transmission.

The communication system related to this invention is characterized bytheoretically having a relation of Tr=Tp between the transmission periodTp and the timing pulse period Tr.

This produces an effect that the data stored in the microcomputer on thereceiving side can substantially be read out and processed.

The communication system related to this invention is characterized inthat the relation between the transmission period Tp and the timingpulse period Tr is set in such a manner that at least a piece of datareadable from the memory is included in a period between a timing pulseand the next timing pulse.

With this, a piece of data can always be read out and processed for eachtiming pulse, and there is an effect that the accuracy of the readingprocess can be increased.

The communication system related to this invention is characterized bytheoretically having a relation of Tr=2Tp between the transmissionperiod Tp and the timing pulse period T.

This produces an effect that the condition setting of the microcomputercan easily be made.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic perspective plan view for explaining thepositional relation between the main ECU and the satellite ECU;

FIG. 2 is a block diagram showing the circuit configuration of theconventional communication system;

FIG. 3 is a signal diagram for explaining the conventional communicationsystem;

FIG. 4 is a block diagram showing the circuit configuration to which thecommunication system according to the embodiment of this invention isapplied;

FIG. 5 is a signal diagram for explaining the start-stop synchronizationcommunication used in the embodiment of this invention;

FIG. 6 is a signal diagram for explaining the communication systemaccording to the embodiment of the present invention;

FIG. 7 is a signal diagram for explaining the signal processing methodof the communication system according to the embodiment of thisinvention; and

FIG. 8 is a signal diagram for explaining another signal processingmethod of the communication system according to the embodiment of thisinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

Now, to describe this invention in more detail, the best embodiment ofthis invention is described according to the accompanying drawings.

First Embodiment

FIG. 4 is a block diagram showing the schematic circuit configuration towhich the communication system according to a first embodiment of thisinvention is applied. This figure is different from FIG. 2 in the pointthat the communication circuits (25 and 35 in FIG. 2) are notrespectively provided outside the microcomputers 23 and 33. Accordingly,the construction and operation are similar to the description of FIG. 2except for the point that signals are exchanged in a different waybecause the communication system is different, so that duplicatedescription of it is omitted here.

The microcomputer generally has a data signal generation function of thestart-stop synchronization communication. This data signal has a datatime that repeats in a fixed cycle, as described later. In thisembodiment, the start-stop synchronization communication function of themicrocomputer is used.

In FIG. 4, the microcomputer first microcomputer) 33 outputs the faultdiagnosis data on the lateral acceleration sensor 34 and theacceleration switch 37 as well as the determination data on aside-impact collision by carrying them on a data signal of thestart-stop synchronization communication. The output signal istransmitted to the main ECU 20 via the communication interface 36. Inthe main ECU 20, the data signal is received through the communicationinterface 26 and provided to the microcomputer (second microcomputer)23. In the microcomputer 23, the data contained in the received signalis sequentially read into the memory. This data is read by timing pulsesfor reading which have a predetermined period, and used to determine thecollision diagnosis and collision status.

In FIG. 5, an example of the data frame of the data signal used in thestart-stop synchronization communication is shown. Regarding the numberof bits assigned, the start bit is assigned one bit, the data bits areassigned eight bits of b0 to b7, the parity is assigned one bit, and thestop bit is assigned one bit, which are constructed in this order. Thefault diagnosis data, collision data, and other necessary data arerepresented by the data bits b0 to b7 of the signal. However, the numberof data bits is not limited to eight, and it is determined by themicrocomputer used.

FIG. 6 shows the relation between the data transmission period Tp andthe data time (time of data frame) Td of the signal used in thestart-stop synchronization communication.

For the case of Td>Tp/2, the transmission data signal from themicrocomputer 33 has a time allocation as shown in (a). A noise may beincluded in a non-data time band as shown in (b). If this occurred, themicrocomputer 23 of the main ECU 20 would erroneously detect the noiseas the start bit, and start to read data. Assuming that the data readtime is the same as the original data time Td, if a data change from 1to 0 occurred after the end of the reading, the microcomputer 23 wouldagain erroneously detect it as the start bit to start the readoperation. If this error operation is repeated, it takes time for thenormal receive state to be recovered, and the recovery can be impossibleunder certain circumstances.

Thus, in the first embodiment, the data transmission period Tp and thedata time Td are set so as to have a relation of Td<Tp/2 shown in FIG. 6(c). By this, even if reading due to a wrong detection by themicrocomputer 23 occurs when a noise is included, as shown in (d), thenormal receive state can be recovered at least on around the third time.

When a data signal having the transmission period Tp as described aboveis received at the microcomputer 23, it is stored in the built-in memoryof a predetermined capacity while being sequentially renewed. Each ofthe data accumulated in the memory is read out in response to timingpulses for reading which repeat with a predetermined period Tr, andsubject to data processing. The relation between the timing pulse periodTr and the transmission period Tp is described according to the signaldiagrams shown in FIGS. 7 and 8.

Assuming that the timing pulse period Tr is fixed, the transmissionperiod Tp is set by the microcomputer 33. Both periods Tr and Tp arepreferably set to the same value, but actually it is almost impossibleto make them the same because of variations in the frequency of theoscillator to be used. Accordingly, the two periods Tr and Tp aresomewhat different from each other, and have a relation of Tp>Tr asshown in f 7 (a) or Tp<Tr as shown in FIG. 7 (b).

For the case of Tp>Tr, the timing pulses p1 and p2 for reading can readrespective data d1 and d2, but the timing pulse p3 cannot read data d3,because it has not completely been stored in the memory. Instead, it isthe timing pulse p4 that reads the data d3, and the processing delaysaccordingly.

Further, for the case of Tp<Tr, the timing pulse p1 cannot read the datad1, which is read by the pulse p2. The data d2 is not used, because thepulse p2 has read the data d1 once. The next timing pulses p3 and p4will read the data d3 and d4 in sequence. Thus, time t1 is generatedwhere reading and data processing are not performed.

As described above, by theoretically setting the timing pulse period Trand the transmission period Tp to the same value, though they actuallydiffer from each other, the determination function of the microcomputer23 can effectively be achieved. However, to further increase theaccuracy of it, and to take into consideration the construction of asimple circuit, the data transmission period Tp is preferablytheoretically set ½ times the timing pulse period Tr. In this case, therelation between the two also actually fluctuates a little, and itbecomes 2Tp>Tr as shown in FIG. 8 (a) or 2Tp<Tr as shown in FIG. 8 (b).

For the case of 2Tp>Tr, the timing pulses p1, p2, p3, and p4 read andprocess the data d1, d3, d4, and d6 existing between the respectivepulses. The timing pulse can read out and process any data without fail.

Further, for the case of 2Tp<Tr, the timing pulses p1, p2, p3, and p4also read and process the data d1, d3, d6, and d8 existing between therespective pulses without fail. The latest data is read and processed.Further, even if a time t2 occurs in which no data is read andprocessed, it is shorter than the time t1 in FIG. 7 (b).

As described above, in accordance with the first embodiment, since faultdiagnosis and collision data are directly transmitted to themicrocomputer 23 of the main ECU 20 by using the data signal forstart-stop synchronization communication provided in the microcomputer33 of the satellite ECU 30, and processed by using the processingfunction of the start-stop synchronization communication, no triggersignal is required, so the device can be made small-sized withoutproviding any specific transmitter-receiver circuit, and the processingbecomes simple because data reception is automatically carried out.

Further, in accordance with the first embodiment, the data time Td andthe transmission period Tp of the data signal are set in such a relationof Td<Tp/2, and thus, the time taken for the detection operation torecover the normal reception on the receiving side can be shortened evenif a noise is included.

Further, in accordance with the first embodiment, by setting thecondition between the transmission period Tp of the data signal and theread timing pulse period Tp of the microcomputer 23 of the main ECU 20,the processing accuracy can be increased. In particular, if the relationbetween the transmission period Tp and the timing pulse period Tr isestablished such that at least one piece of data readable from thememory is included between a timing pulse and the next timing pulse, theprocessing is made effective. Specifically, to enable easy setting onthe condition setting of the microcomputer and reduce as much aspossible the data that is not read, the relation of 2Tp=Tr ispreferable.

INDUSTRIAL APPLICABILITY

As described above, the communication system related to this inventionenables the actual circuit assembly to be made simple by using thecommunication function normally provided to the microcomputer, namelythe start-stop synchronization communication function, and thus, itcontributes to downsizing the circuit and maintenance can easily becarried out. Accordingly, it is desired that the system is put in apractical use with the vehicular occupant protecting device, which hasincreasingly been permanently provided in recent years.

1. A communication system comprising: a first microcomputer having a communication function for outputting a data signal including data frames, each including a plurality of data bits and having a data time Td and a transmission period Tp; and a second microcomputer for receiving said data signal, sequentially storing said data frames in a memory, and reading and processing said data frames by timing pulses, wherein said data time Td and said transmission period Tp have a relation of Td<Tp/2, and the transmission period Tp is substantially equal to Tr/2, where Tr is a timing pulse period of the timing pulses.
 2. The communication system according to claim 1, wherein the relation between the transmission period Tp and the timing pulse period Tr of the timing pulses is set in such a manner that at least a piece of data readable from the memory is included in a period between a timing pulse and a next timing pulse. 